On Thu, Aug 13, 2026 at 2:34 AM Hao Ge <[email protected]> wrote:
>
> codetag_needs_module_section() is called twice per codetag section, once
> in layout_sections() and once in move_module(), and both depend on
> mem_profiling_support, which changes without a lock. If profiling is
> disabled between the two calls, layout excludes the section (offset 0)
> while move copies it as normal memory to offset 0:
>
> CPU0 (insmod A) CPU1 (insmod B)
> ---------------- ----------------
> layout_sections()
> needs_section_mem() == true
> sh_entsize: type, offset = 0
> reserve_module_tags() overflows
> shutdown_mem_profiling()
> mem_profiling_support = false
> move_module()
> needs_section_mem() == false
> offset = sh_entsize & MASK = 0
> memcpy(mod->mem[type].base + 0, ...)
> -> overwrites the first section there
>
> Record the decision in layout_sections() in sh_entsize using a
> MOD_MEM_CODETAG type, and have move_module() use that instead of asking
> again.
>
> reserve_module_tags() returns -EAGAIN if profiling was disabled after
> layout, so the loader retries and places the section as normal memory.
>
> Fixes: 4835f747d3ed ("alloc_tag: support for page allocation tag compression")
> Signed-off-by: Hao Ge <[email protected]>
> ---
> include/linux/module.h | 11 +++++++++++
> kernel/module/main.c | 17 ++++++-----------
> mm/alloc_tag.c | 8 ++++++++
> 3 files changed, 25 insertions(+), 11 deletions(-)
>
> diff --git a/include/linux/module.h b/include/linux/module.h
> index 7566815fabbe..a02016528e1d 100644
> --- a/include/linux/module.h
> +++ b/include/linux/module.h
> @@ -328,6 +328,17 @@ enum mod_mem_type {
> MOD_INVALID = -1,
> };
>
> +/*
> + * If CONFIG_CODE_TAGGING is on, modules get a .codetag section.
> + * codetag_needs_module_section() says where it goes: the usual
> + * mod->mem[], or off to the codetag region.
> + *
> + * Mark the codetag-region ones with MOD_MEM_NUM_TYPES.
> + * It's just past the real types, so it doesn't index into mod->mem[]
> + * and for_each_mod_mem_type() skips it.
> + */
> +#define MOD_MEM_CODETAG MOD_MEM_NUM_TYPES
Ok, it feels a bit hacky but it's probably the simplest way to mark
codetag regions.
> +
> #define mod_mem_type_is_init(type) \
> ((type) == MOD_INIT_TEXT || \
> (type) == MOD_INIT_DATA || \
> diff --git a/kernel/module/main.c b/kernel/module/main.c
> index ed26f167be84..2337bf604f58 100644
> --- a/kernel/module/main.c
> +++ b/kernel/module/main.c
> @@ -1728,11 +1728,8 @@ static void __layout_sections(struct module *mod,
> struct load_info *info, bool i
> * preallocated contiguous memory.
> */
> if (codetag_needs_module_section(mod, sname,
> s->sh_size)) {
> - /*
> - * s->sh_entsize won't be used but populate
> the
> - * type field to avoid confusion.
> - */
> - s->sh_entsize = ((unsigned long)(type) &
> SH_ENTSIZE_TYPE_MASK)
> + s->sh_entsize = ((unsigned
> long)MOD_MEM_CODETAG
> + & SH_ENTSIZE_TYPE_MASK)
> << SH_ENTSIZE_TYPE_SHIFT;
> continue;
> }
> @@ -2815,11 +2812,10 @@ static int move_module(struct module *mod, struct
> load_info *info)
> continue;
>
> sname = info->secstrings + shdr->sh_name;
> - /*
> - * Load codetag sections separately as they might still be
> used
> - * after module unload.
> - */
> - if (codetag_needs_module_section(mod, sname, shdr->sh_size)) {
> +
> + enum mod_mem_type type = shdr->sh_entsize >>
> SH_ENTSIZE_TYPE_SHIFT;
> +
> + if (type == MOD_MEM_CODETAG) {
> dest = codetag_alloc_module_section(mod, sname,
> shdr->sh_size,
> arch_mod_section_prepend(mod, i),
> shdr->sh_addralign);
> if (WARN_ON(!dest)) {
> @@ -2832,7 +2828,6 @@ static int move_module(struct module *mod, struct
> load_info *info)
> }
> codetag_section_found = true;
> } else {
> - enum mod_mem_type type = shdr->sh_entsize >>
> SH_ENTSIZE_TYPE_SHIFT;
> unsigned long offset = shdr->sh_entsize &
> SH_ENTSIZE_OFFSET_MASK;
>
> dest = mod->mem[type].base + offset;
> diff --git a/mm/alloc_tag.c b/mm/alloc_tag.c
> index 461fa87fbb0b..7481180dadd2 100644
> --- a/mm/alloc_tag.c
> +++ b/mm/alloc_tag.c
> @@ -893,6 +893,14 @@ static void *reserve_module_tags(struct module *mod,
> unsigned long size,
> if (size < sizeof(struct alloc_tag))
> return ERR_PTR(-EINVAL);
>
> + /*
> + * Profiling may have been disabled by a concurrent module load.
> + * Return -EAGAIN so the loader retries with profiling off, laying
> + * the section out as ordinary module memory.
> + */
> + if (!mem_profiling_support)
> + return ERR_PTR(-EAGAIN);
I think this requires your patch [1] from another patchset to work
correctly, correct? If so, I would suggest sending this patch as part
of that patchset since there is a dependency.
[1] https://lore.kernel.org/all/[email protected]/
> +
> /*
> * align is always power of 2, so we can use IS_ALIGNED and ALIGN.
> * align 0 or 1 means no alignment, to simplify set to 1.
> --
> 2.25.1
>
